Craniopharyngioma Imaging: An Overview

Introduction:

The central nervous system is considered a processing center as it controls and regulates the physiological processes of the body. It mainly comprises the brain and the spinal cord. The brain is a vital organ that controls speech, touch, memory, vision, temperature, and other essential body functions. The brain comprises many glands and a rich vascular supply. One such important brain structure is the pituitary gland (also known as the master gland). It regulates the entire body mechanism by governing the functions of other glands and the hormones secreted by them.

A tumor is an abnormal growth or cellular mass occurring in the body. An abnormal growth occurring in any part of the brain is termed a brain tumor. Brain tumors can be benign (non-cancerous) or malignant (cancerous). However, any tumor within the brain can be potentially fatal as they tend to grow in an enclosed space (within the skull), thereby compressing nearby anatomic structures or increasing the pressure within the skull. Brain tumors can primarily originate in the brain or metastasize, where it has spread from other organs.

What Is Craniopharyngioma?

Craniopharyngioma is a benign brain tumor occurring near the pituitary gland. It is a rare entity that may arise in children and adults. Craniopharyngiomas, though benign, can cause potential complications as they grow. They tend to compress the pituitary gland and other adjacent structures, affecting the functioning of the brain. Symptoms include persistent headache, altered vision, fatigue, and vomiting. In children, it affects their cognitive and functional abilities resulting in growth retardation. Craniopharyngiomas rarely become malignant; however, they behave aggressively in their tendency to recur frequently.

What Are the Causes of Craniopharyngioma?

The development of craniopharyngiomas has two significant theories giving rise to subtypes -

• Adamantinomatous Craniopharyngioma - This is a common subtype and can affect all age groups. Most pediatric craniopharyngiomas are of this subtype. During the development of the embryo, the craniopharyngeal duct gives rise to the anterior pituitary. When the remnants of this duct undergo a certain cellular transformation, it results in adamantinomatous craniopharyngioma.

• Papillary Craniopharyngioma - This subtype is most commonly seen in adults. They have a metaplastic origin, which is when another cell type completely replaces one cell type.

What Are the Symptoms of Craniopharyngioma?

Craniopharyngiomas mainly occur in the sella (depression in the skull bone containing the pituitary gland). The symptoms are due to the compression of the pituitary gland or adjacent structures by the tumor mass. They are described below -

• Headaches are common due to increased intracranial pressure.

• Altered vision.

• Nausea and weakness.

• Growth retardation in children.

• Cognitive abnormalities (intellectual challenges).

• Delayed puberty.

• Diabetes insipidus (disorder resulting in a fluid imbalance in the body).

• Obstructive hydrocephalus (fluid accumulation in the brain).

What Are the Various Imaging Modalities of Craniopharyngioma?

Imaging is essential to locate the tumor and assess the severity of damage which could subsequently guide the treatment plan. In addition, the extent of vital structures involved could delineate the mode of treatment to a great extent. Imaging techniques can also help in differentiating craniopharyngioma from other tumors that could occur in the same region. The imaging modalities are described below -

1. Radiography -

• X-rays are a non-specific diagnostic test to image craniopharyngiomas.

• Craniopharyngiomas may present as calcifications or expansion of the cranial bone containing the pituitary gland.

• However, these calcifications may also be found in other conditions, such as aneurysms (abnormal weakening and bulging of the blood vessel); hence it is difficult to distinguish a craniopharyngioma from an aneurysm.

• Smaller calcifications may be missed on X-rays.

• Also, X-rays are not ideal for visualizing soft tissue masses. Hence, X-rays are not confirmatory to diagnose craniopharyngiomas.

2. Computed Tomography (CT) -

• CT can be used to diagnose the size of the tumor and the calcifications associated with it.

• CT can also be used post-operatively for follow-up.

• Non-enhanced CTs are more specific.

• Micro-CT scan is a recent advancement that can provide a three-dimensional picture of the tumor invasion.

• The adamantinomatous craniopharyngioma appears predominantly as a cystic lesion with a solid component containing calcifications.

• The bone containing the pituitary gland may be expanded.

• Hydrocephalus may be prominent.

• Papillary craniopharyngiomas are usually solid but devoid of calcifications. However, they may occasionally appear as soft tissue mass within the ventricles of the brain.

• The optic chiasm (where the optic nerves supplying the eyes cross over) is usually displaced, resulting in visual disturbances.

• However, the papillary variant may miss being diagnosed in the CT.

3. Magnetic Resonance Imaging (MRI) -

• MRI is the gold standard tool to diagnose craniopharyngiomas.

• It can precisely detect the size and extent of the tumor. In addition, both solid and cystic areas can be clearly distinguished in MRI.

• Magnetic resonance spectroscopy is more accurate in defining cystic lesions.

• Bony expansion, hydrocephalus, and compression of the third ventricle are predominant features of craniopharyngiomas. In addition, the third ventricle compression helps differentiate craniopharyngiomas from other benign tumors, such as pituitary adenoma or Rathke cleft cyst.

• However, MRI cannot be used in patients with cardiac pacemakers or any foreign body metallic implants.

• Also, the contrast agent used in MRI is gadolinium-based which is highly nephrotoxic. Hence, it is completely contraindicated in patients with end-stage renal diseases.

• Due to the overlapping features, CT and MRI may not be sufficient to differentiate craniopharyngiomas from aneurysms. Angiography may be warranted.

4. Angiography -

• CT angiography and MR angiography are primary diagnostic aids and essential tools in distinguishing aneurysms from craniopharyngiomas.

• The displacement of the blood vessels due to the impinging mass can be seen in angiography.

• Displacement of the optic chiasm can also be noticed.

5. Ultrasonography -

• Due to the wide availability and easy accessibility of CT and MRI, ultrasonography has not had much diagnostic importance in craniopharyngiomas.

• However, color doppler has proved beneficial, though not 100% specific, in prenatal diagnosis of craniopharyngiomas in the fetus.

What Is the Mode of Treatment for Craniopharyngiomas?

Surgical removal of the tumor remains the mainstay in treating craniopharyngiomas. However, it is challenging as the tumor is usually located close to prominent neurovascular structures. Therefore, radiotherapy and chemotherapy have also been successfully used in treating craniopharyngiomas.

Conclusion:

Craniopharyngiomas are benign brain tumors presenting a wide array of symptoms. The primary goal of imaging craniopharyngioma is to determine the precise location and extent of the disease. It also helps to assess the proximity of the lesion to adjacent vital structures within the brain. A multidisciplinary team approach is required in treating craniopharyngiomas considering its central location. Though the prognosis is excellent, craniopharyngiomas are deemed to have a high recurrence rate.